1,3-Cyclobutadiene (C₄H₄) is a highly reactive and unstable organic compound that consists of a four-membered carbon ring with alternating single and double bonds, specifically at the 1 and 3 positions. Due to its antiaromatic nature — having 4 π-electrons in a conjugated planar system — it experiences significant electronic instability, which leads to rapid dimerization or reaction with other species under standard conditions. The molecule exists transiently in the gas phase or at very low temperatures and has a rectangular rather than square geometry, as predicted by molecular orbital theory to relieve some of the antiaromatic strain. 1,3-Cyclobutadiene is of considerable interest in theoretical and organometallic chemistry, particularly in studies of aromaticity, bonding, and as a ligand in metal complexes where its stability can be enhanced through coordination.